1. Field of the Invention
The present invention relates generally to fiber optics or photonics modules and more particularly to micro-photonics modules having a high degree of precision and integrating many components onto a single substrate.
2. Description of the Related Art
Optical communications systems are widely used for carrying large amounts of information using light and optical fibers in place of the electric current and metal wires found in older communications systems. These optical communications systems can also carry greater amounts of information with lower data loss and lower cost over great distances than the older metal wire system. For this reason, considerable development has been done on components of optical communication systems, such as photonics packages or modules.
Photonics generally refers to devices that have both electronic and optical attributes. Photonics modules include the optical parts necessary to transmit, receive, or process the light that carries the information through the optical fiber. The photonics devices that are part of the photonics modules include lasers, which generate coherent light in response to an electronic signal, and photo detectors, which generate an electronic signal in response to light. These are the devices typically used to transmit, receive, and process the optical information that travels along the optical fibers. These photonics devices, however, cannot work efficiently without the help of other optical parts that together make up the photonics module.
Typically, photonics modules use edge-emitting semiconductor lasers for transmitting, and surface-detecting photo detectors for receiving, the light that carries the information through the optical fibers. Edge-emitting lasers have a relatively wide radiation angle, however. The radiation angle is the angle of the "cone" of light that radiates from the edge-emitting laser. Therefore transmitter modules typically have a lens inserted between the laser and the optical fiber for focusing the laser light to obtain high efficiency in optical coupling. Likewise, light leaving an optical fiber has a radiation angle. Thus, a lens is also typically inserted between the optical fiber and a surface-detecting photo detector in a receiver module for focusing the light to obtain high coupling efficiency. Using a lens has the additional benefit that it enables the distance between different elements of the photonics modules to vary from module to module according to the design objectives.
Other optical components, such as filters, isolators, or mirrors may also be inserted between the edge-emitting laser and the optical fiber in a transmitter module. These components may serve many functions depending on the design and intended function of the specific photonics module. For example, it is desirable to insert an optical isolator between the laser and the optical fiber. The optical isolator allows the laser light to pass freely through in one direction on its way to an optical fiber, but prevents laser light coming from the optical fiber from returning to the laser. Similarly, other optical components may be inserted between the photo detector and the optical fiber in a receiver module.
In a photonics module it is desirable that the laser, lens, optical component and optical fiber be in a precise predetermined alignment with one another. Likewise, it is desirable for the optical fiber, lens, optical component and photo detector to be in a precise predetermined alignment with one another in the receiver module. To achieve this precise alignment, three-dimensional fixtures or mounts are typically needed to hold the components in place and in alignment with one another.
One disadvantage of such conventional photonics modules or packages is that the fixtures are costly to fabricate because they require relatively high precision. Another disadvantage is that assembling the components of the photonics modules into precise positions using the fixtures is time consuming, which causes low throughput in production. In addition, considerable time and care may also be needed for alignment and adjustment while assembling the photonics modules. Finally, the modules must be completely assembled into their final packaging before they can be tested. This limits the ability of the photonics modules to be inexpensively mass produced by operators having a moderate level of skill. It also results in the production of unserviceable modules. These factors typically prevent the production of low-cost photonics modules.
One way has been developed to keep a lens and a photonics device in a precise and predetermined alignment, solving many of the previously experienced problems. In copending U.S. patent application Ser. No. 08/705,867, titled "An Improved Micro-Photonics Module," now U.S. Pat. No. 5,771,323 assigned to the assignee of the present invention and incorporated herein by reference, there is described a pyramidal cavity, including a frustopyramidal cavity, precision formed in a mounting member. The purpose of the pyramidal cavity is to precisely locate a ball lens. The ball lens is set in the cavity in precise alignment with the photonics device.
When optical components, such as filters, isolators, or mirrors are desired in the photonics module, however, specialized fixtures are needed to keep the optical component precisely aligned with the lens, the photonics device, and the optical fiber. Thus, photonics modules including optical components have many of the same disadvantages as the conventional photonics modules that required specialized fixtures.